An insulin-like material characterized by radioimmunoassay, gel filtration and bioactivity in fat cells can be found in eukaryote and prokaryote organisms. In addition to insulin a few other hormones- ACTH and somatostatin have been characterized in unicellular organisms. These findings suggest that the origins of the endocrine system appeared earlier than previously thought. We are also continuing the studies on extrapancreatic insulin found in the guinea pig.